This application claims the priority of German priority document 100 06 781.6, filed 18 Feb. 2000 (18.02.2000) (PCT International Application No. PCT/EP01/00879), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel cell apparatus for producing electrical power that is distributed to electrical loads in a high voltage line network, and to further electrical loads in a low-voltage line network that is connected to the high-voltage line network via at least one DC/DC converter. In addition to the loads, the low voltage network contains at least one rechargeable battery.
Mobile devices, such as vehicles with a fuel cell for producing electrical power, often have two electrical line networks. A high-voltage network, which is fed from the fuel cell, contains the relatively high-power loads, such as one or more traction motors and loads which are required for operating the vehicle when at rest or when in motion, as well as electrical drives for auxiliary equipment for starting and for operating the fuel cell (for example, a PEM fuel cell). The second network is a low-voltage network with relatively low-power electrical loads that are switched on as required during motion or when the mobile device is at rest. The low-voltage network is also connected to drives and other loads, such as heating circuits or a battery, which are required for starting the fuel cell.
The low-voltage network contains a rechargeable battery which supplies electrical power to the appropriate loads for starting the fuel cell. Bidirectional DC/DC conversion is provided between the two networks and, during operation, supplies charging current from the fuel cell for the rechargeable battery and, when required, operating current for loads that are connected in the low-voltage network. While one pole of the low-voltage network is connected to the mobile apparatus ground, the high-voltage network is electrically isolated.
One object of the invention to provide a compact appliance which can be handled on its own and can be installed in an apparatus such that it can be replaced.
Another object of the invention is to provide such a system that carries out monitoring functions for electrical variables, distribution functions for the loads and disconnection functions in order to prevent damage in the event of critical operating states.
Still another object of the invention is to provide an arrangement for switching functions during the phases in which the fuel cell is being started and switched off, for the fuel cell, for the loads and for the line network, in the apparatus which contains a fuel cell for producing power and contains at least one network with electrical loads that are supplied with power from the fuel cell.
These and other objects and advantages are achieved by the apparatus according to the invention, which has at least one fuel cell for producing electrical power that is distributed to electrical loads in a high-voltage power network connected to the fuel cell, and to further electrical loads in a low-voltage power network that is connected to the high-voltage power network via at least one DC/DC converter, and contains at least one rechargeable battery. A separable central monitoring and switching unit has a housing that can be detachably connected to the fuel cell housing. Conductors connected to an electrical outputs or poles of the fuel cell are arranged via dust-tight and water-tight bushings in the wall of the housing and detachable contact means. At least one such conductor includes a contact of a fuel cell circuit breaker in the course of the line. Branches run from the conductors, which are provided with fuses in at least one pole, to dust-tight and water-tight bushings in a housing wall with detachable contact means connected to lines from loads that are supplied with power from the fuel cell. One branch from the low-voltage line network runs via a dust and water-tight bushing to a control and evaluation unit which is associated with the central monitoring and switching unit and is connected to sensors for detecting the operating states of the fuel cell and of the electrical line networks. Such branch also runs via dust and water-tight bushings and easily detachable contact means in or on a housing wall, to sensors which detect operating states of the mobile apparatus. The control and monitoring unit closes the fuel cell circuit breaker once the fuel cell has been started and has reached its operational readiness. Upon detection by the sensors of the occurrence of certain predetermined critical operating states, for which the supply of power to the high-voltage line network must be connected or disconnected, the control and monitoring unit opens the fuel cell circuit breaker.
The functions which are essential for controlling and monitoring the electrical line networks and their loads are carried out by components in an appliance which can be extended and can be checked separately. Fast functional testing and fault localization are thus possible. The appliance can be manufactured at low cost as a separable unit and can be installed in the mobile device quickly and easily, with bushings preventing the ingress of moisture. Operation of the appliance is thus not adversely affected, even when located in a moist atmosphere. A suitable control and evaluation unit is known, such as for example as disclosed in German Patent Application 199 500 08.8. Reference is hereby made to this patent application from the same applicant.
The control and evaluation unit can be arranged in the interior of the housing, together with the other components of the central monitoring and switching unit, and can be handled as a component of the central monitoring and switching unit. The other components of the monitoring and switching unit form a switching and distribution unit. In a preferred embodiment, the control and evaluation unit is arranged in its own housing, which has the bushing for the branch for the low-voltage network and the bushings for the easily detachable contact means in or on the housing wall for the line connections for the sensors for detecting the operating states.
In one of the housing walls, plug connectors are arranged with connections for lines that connect the control and evaluation unit to the sensors for detecting the operating states of the fuel cell and of the electrical line networks. In this case, the dedicated housing can be detachably mounted, as a cover for an opening on the housing which can be attached to the fuel cell housing. In this embodiment, the control and evaluation unit forms a separate unit, and can be installed and disconnected even without disconnecting the central monitoring and switching unit. That is, this unit can also be produced, tested, stored and transported, which is advantageous, at least with regard to spares stockholdings.
It is particularly advantageous for the housing of the control and evaluation unit to be thermally insulated from the housing with the components of the switching and distribution unit. The control and evaluation unit may therefore contain electronic components whose operating temperature is not significantly adversely influenced by the operating temperature of the fuel cell. For example, large-scale integrated electronic circuits such as processors may be provided in the control and evaluation unit.
In one especially advantageous embodiment, the control and evaluation unit has a printed circuit board which is provided with electronic components and is arranged in the interior of a trough-shaped cover that covers the housing (which is open on one side), with the components of the switching and distribution unit. A thermally insulating insert is provided in front of the opening in the housing. In this embodiment, when the housing is open, both the interior of that part of the monitoring and switching unit which has the power distribution, fuse and switching elements (that is, the switching and distribution unit) and the control and evaluation unit in the cover are easily accessible, considerably simplifying the fuel cell system and facilitating testing, inspection and maintenance.
The apparatus is preferably designed to be mobile. In particular, the apparatus is a motor vehicle which is supplied with power from a fuel cell. However, it may also be any other mobile apparatus, such as a boat, ship, locomotive, prime mover or the like.
The water-tight bushings and the easily detachable contact means are preferably in the form of water-tight plug connectors. The plug connectors are secured in particular by means of “interlock” connections against being mated and disconnected while on load. These plug connectors allow not only quick connection and disconnection of the contacts, but also protect against the ingress of dust, water or moisture into the housing interior.
One other option is to provide water-tight line bushings which, at least at their ends outside the housing, have cable lugs for attachment to the associated ends of the line networks.
In one preferred embodiment, the control and evaluation unit is connected to gas sensors arranged outside the housing, for the detection of leaks in units which produce hydrogen, store hydrogen or carry hydrogen, to a sensor, which is arranged in the housing with the power distribution, fuse and switching elements, for the fuel cell current. It is also connected to at least one sensor arranged outside the monitoring and switching unit, for detecting an impact between the mobile device and an obstruction; to an arrangement situated in the housing with the power distribution, fuse and switching elements, for measuring the insulation resistance of the electrically insulated line network; and to a sensor which is arranged inside the monitoring and switching unit, for the fuel cell voltage, and opens the fuel cell circuit breaker upon detection of a measured value that is undesirable or unacceptable for safety reasons. The control and evaluation means, which are provided for operational safety and reliability of the fuel cell system and of the line network, are protected in housings, in this embodiment. When such a measured value such is detected, the control and evaluation unit opens the fuel cell circuit breaker to interrupt the power output from the fuel cell, such that the line network together with the electrical loads is changed to a safe operating state. This avoids any danger to personnel, parts of the apparatus itself, as well as the entire apparatus with the fuel cell system and the environment. In one particularly expedient embodiment with a monitoring and switching unit to which a control and evaluation unit having a housing in the form of a cover is connected, plug connectors which disconnect the lines to the loads when the cover is disconnected are arranged on the cover edges. In this case the housing, which is in the form of a cover, can be connected by means of plug connectors to the lines to the loads. When the cover is removed, the voltage is disconnected from the lines to the loads, provided that the loads do not include an energy store, such as a battery or a capacitor.
The control and evaluation unit monitors, in particular, the fuel cell output current for overshooting a predeterminable limit value. It can also monitor the current of the electrical drive and the voltages of the fuel cell and possibly monitors the low-voltage network for overshooting or undershooting predeterminable limit values and monitors the insulation resistance for undershooting a predeterminable value.
It is expedient for the housing to be arranged at a point in the mobile device such that mechanical destruction of the mobile device has little or no effect on it.
The control and evaluation unit preferably comprises integrated circuits arranged on a printed circuit board in the housing. The conductors and branches in the housing interior may be in the form of a cable harness, conductors using stamped grid technology, conductor tracks on a printed circuit board (for example, a multilayer printed circuit board), copper rails, or flexible circuit technology. The nature of the conductors and branches depends on the magnitudes of the currents which are being distributed. Two or more of the techniques mentioned above may also be used in the housing.
In one preferred embodiment, the fuel cell can be switched off, in particular by detachable contacts, via a line which can be disconnected from the connection to the fuel cell housing when the housing is removed. This embodiment is a safety circuit. The safety circuit can be formed by a link via two plug contacts, or may be in the form of a separately routed line to the high-voltage supply.
It is particularly expedient for the housing of the monitoring and switching unit and/or the fuel cell housing to have centering or guide means for interlocking attachment of the housing to the fuel cell housing. The housing can thus be fitted to the fuel cell quickly and easily, in the position in which it is held.
The housing of the monitoring and switching unit can be screwed to the fuel cell housing, or can be attached by latching means. The mechanical attachment of the housing to the fuel cell housing is physically simple, and can thus be produced or detached easily.
Direct attachment of the housing of the monitoring and switching unit to the fuel cell housing results in short line sections between the electrical outputs of the fuel cell and the fuel cell circuit breaker, which is in the form of a power switch. The joining direction of the housing may be chosen to match the available space on the fuel cell, at an easily accessible point. The housing of the central monitoring and switching unit can be attached to the fuel cell housing in a particularly rigid manner. There is no need for it to be held in a particular manner on other parts of the mobile device. The coupling of the housing to the fuel cell housing means that the retention of the fuel cell housing in the mobile device is sufficient for both housings, so that the housing of the monitoring and switching unit is coupled, in terms of vibration and oscillations, to the fuel cell.
The nature of the attachment and the location of the housing of the monitoring and switching unit allow the housing to be fitted and removed easily and quickly. Servicing and repair work can thus be carried out not only with the monitoring and switching unit installed but also with it removed. The monitoring and switching unit can be installed and removed without removal of other parts of the mobile unit.
It is expedient for a dedicated housing, or at least a compartment for fuses in the conductors and their branches, to be arranged within the housing of the monitoring and switching unit and to be accessible through a sealable opening in the housing of the monitoring and switching unit. With this construction, fuses can be replaced easily and quickly, without having to remove the housing. The fuse holders are, in particular, mounted on a printed circuit board. Depending on the size of the line cross sections of the lines running to the fuse holders, and on the number of fuses, it is also possible to use insulated lines, stamped grids composed of electrically highly conductive materials, conductor rails or flexible circuits with conductor tracks. The fuses for the high-voltage line network are preferably arranged in the fuse housing, and are accessible via an opening, which can be sealed, from outside the housing of the monitoring and switching unit. This opening can be sealed in particular by means of the cover-like housing of the control and evaluation unit. This allows the fuses for the high-voltage line network to be accommodated in a safe and sealed manner. The compartment with the fuses for the branches of the high-voltage network expediently has an additional cover in the housing of the central monitoring and switching unit. This provides safety against accidentally touching them after opening the housing of the monitoring and switching unit.
The fuses are expediently arranged on a printed circuit board under the cover, which can be sealed, of the housing of the central monitoring and switching unit.
The low and high-voltage line networks are DC networks, and have two poles. Since one pole of the low-voltage line network is connected to the mobile device ground, a single-pole fuse is sufficient for the network and load lines. The branches and loads in the high-voltage line network may have single-pole or two-pole protection.
The drive motor or motors for the propulsion system as well as the upstream converter and other electrical loads are protected, in particular, in the interior of the monitoring and switching unit.
If a particularly rugged housing is required for the monitoring and switching unit, it may be made from metal, which offers the additional advantage of good thermal conductivity, so that heat produced in the housing is efficiently dissipated. The amount of heat emitted to the exterior can be increased further by means of cooling ribs or heat exchangers in some other form.
A very strong housing can also be made from a high-strength resistant plastic, which also reduces its weight. A housing such as this is expediently composed partially of metal, if the heat is intended to be dissipated to the exterior via the highly thermally conductive metal. The housing section which is composed of metal has, in particular, cooling ribs.
In a further preferred embodiment, the housing of the monitoring and switching unit has a switch, for example a microswitch, or sensors on housing openings, which responds when the housing cover is opened, opening the fuel cell circuit breaker by interrupting its holding current. (The switch on the opening of the housing is arranged, for example, in the circuit of the coil for the fuel cell circuit breaker.) Once the fuel cell circuit breaker has opened, there is no voltage within the housing, except for low-voltage circuits and the line sections from the outputs of the fuel cell to the contacts of the fuel cell circuit breaker. Instead of a switch on the housing cover, it is also possible to use a sensor, for example a light barrier etc. If the control and evaluation unit is arranged in the cover for the housing of the monitoring and switching unit, then there is no current to the fuel cell circuit breaker when the cover is removed, so that the high-voltage line network is not live.
The fuses for the low-voltage line network circuits can likewise be arranged in the housing of the monitoring and switching unit. In this case, they are expediently arranged so that they are accessible from the outside and are separated from the fuses for the high-voltage line network. However, it is also possible to arrange the fuse for the low-voltage line network in an externally accessible housing, separate from the housing of the monitoring and switching unit. The fused switches are, for example, arranged on a printed circuit board. The fuse holders may also be connected to copper rails or to flexible lines or to flexible circuits with conductor tracks. An arrangement in which the connections for the fuse holders use stamped grid technology is likewise possible.
The fuse housing for the low-voltage line network is, by way of example, integrated in the low-voltage line network. However, a separate fuse housing is advantageous, which is externally accessible independently of the housing of the monitoring and switching unit.
The DC/DC converter device, which is arranged for example between the high and low-voltage line networks as a bidirectional converter, may require a precharging current in order to start to operate. The precharging components may be arranged in the housing of the monitoring and switching unit. If no precharging option is required, the space reserved for these components in the housing remains free. Another advantageous arrangement for the equipment of the monitoring and switching unit is for the components to be installed in their own housing, which can be fitted externally to the housing of the monitoring and switching unit, with water-tight bushings and plug connectors being provided for the electrical connection in the two housings.
The fuel cell circuit breaker for isolating the fuel cell from the loads and from a hybrid battery or supercapacitor may have two poles, with both poles being circuit breaker poles for interrupting short-circuits. However, it is also possible to design the contact for only one pole to switch full-load and short-circuit currents. The other contact is then only in the form of an isolating switch, which does not have to switch high currents. In this case, the second contact can be opened with a certain delay with respect to the first contact, since the first contact switches higher currents. One contact may then be a switch without contacts, for example a semiconductor switch. A single-pole fuel cell circuit breaker may also be used, which is designed for switching the maximum load current and the short-circuit current.
In order to simplify servicing and repair of components of the mobile device, without danger from live objects, it is expedient to provide a manually operable off switch in the housing of the monitoring and switching unit. In this case, the off switch can be operated from the outside without removing the housing, allowing the high-voltage line network, together with its electrical loads, to be conductively isolated from the fuel cell. It is expedient to provide an additional switch, which is externally accessible, for any hybrid battery or supercapacitor which may be used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.